Securing systems through an air gap is an idea goes back decades, and through the 50s to as recently as the 2000s the idea that you could safely and successfully run and maintain systems by simply not connecting to a network protects them from vulnerabilities may have been true. But in the last ten or more years, I would argue it is a fallacy, that can lull people into a false sense of security and therefore more likely to take more risks (or at least not be as careful as we should be). This idea is a well established piece of psychology with modern cars (here for example). This is known as Risk Compensation (also more here) or an aspect of behaviour adaptation.

Whilst this is rather theoretical, perhaps we should illustrate in practical terms why it is both a fallacy, and in the modern day simply impractical.